Many techniques exist for sensing a constituent gas concentration within a gas sample. Non-dispersive infrared (NDIR) techniques infer the concentration of a constituent gas by measuring the gas sample's ability to absorb electromagnetic radiation. By examining absorption in a wavelength band where absorption is dominated by one constituent gas, relatively simple NDIR sensors can accurately measure concentration of that gas as a function of radiation absorption. For instance, carbon dioxide (CO2) detectors often measure absorption at a 4.2-micron wavelength, where CO2 strongly absorbs. For other gases, other visible or infrared bands can be selected.
To ensure accurate determination of the gas concentrations, a sensor may require periodic calibration. The typical calibration process includes providing a calibration gas with a known concentration to sample chamber via gas port, manually accessing electronics to obtain gas concentration data as each is determined, waiting for the calibration gas to equilibrate within sensor, and manually adjusting one or more controls within sensor electronics to set the measured equilibrium gas concentration equal to the known concentration value of the calibration gas. This process, however, is highly dependent upon the skill of the human technician. For instance, the technician is required to manually access sensor electronics to retrieve the reported gas concentrations in real-time and to manually adjust sensor electronics based on the reported concentration values. The technician typically must perform a real-time mathematical conversion on each reported concentration value, e.g., a conversion from volts [V] or millivolts [mV] to parts per million [ppm]. In some instances, the manual adjustment of sensor can be sensitive and time-consuming, especially if there is a lag time between the adjustment and the corresponding reported gas concentration. The technician must also exercise some judgment as to when the calibration gas has reached equilibrium within sample chamber. Sensor, further, may be inconveniently located such that the technician cannot gain the physical access required to perform the manual calibration.
The invention is an improved calibration system and method of calibrating a gas sensor that automatically calibrates the sensor.